1. Field of the Invention
The invention relates to the production of polyaspartic acid homo- and copolymers by biotechnological processes and to the use of the resulting products (for influencing the crystallization or agglomeration behavior of sparingly soluble salts or solids in aqueous systems).
2. Description of the Related Art
Crystallization and agglomeration processes are, as biological mineralization, among the fundamental processes of animate nature. Thus, they are involved, for example, in the structure of skeletons or shells in living organisms. In nature, these mineralization processes are controlled by naturally occurring proteins and polysaccharides. (S. Weiner, Biochem. 22, (1983), 4139-45; C. S. Sikes, A. P. Wheeler, in Chemical Aspects of Regulation of Mineralisation., Eds. C. S. Sikes , A. P. Wheeler University of South Alabama Publ. Services (1988), 15-20).
Unfortunately, both in nature and in the industrial sector, unwanted mineralization processes also occur and result in tenacious, troublesome deposits and encrustations such as, for example, dental plaque, organ concretions or, in the industrial sector, encrustations on heat exchanger surfaces or cooling towers particle agglomerations in pigment dispersions, encrustations on hard (for example glass metal) and soft (textile) surfaces. In the past, various proposals have been made for exploiting this natural action principle for industrial problems. Thus, the U.S. Pat. Nos. 4,534,881, 4,585,560, 4,587,021 describe the inhibition of calcium carbonate deposits by protein fractions, polysaccharide fractions or polyamino acid fractions from calcium carbonate-forming organisms such as crustaceans etc.
In addition, the inhibition of mineral deposits by polyanionic hydrophobic polypeptides with a block copolymer structure and related phosphorylated polypeptides is claimed in the literature (U.S. Pat. No. 4,868,287). The polypeptides used are prepared by methods of peptide chemistry. WO 92/17194 states that an improved synthesis of these polypeptides is provided.
Since the proteins described above acquire their polyanionic characteristics through a high aspartic acid content, aspartic acid homo- and copolymers are also claimed for this purpose. These polyaspartic acids are, however, all obtained by chemical synthesis. Thus, for example, a polyaspartic acid sodium salt can be prepared by thermal polycondensation of aspartic acid to polysuccinimide and subsequent basic hydrolysis. (Kovacs et al. J. Org. Chem, 26 (1961)1084-1091). Further applications claim the preparation and use of polyaspartic acids by thermal polycondensation of aspartic acid in the presence of acidic catalysts such as phosphoric acid. In addition, polyaspartic acids are also prepared by thermal polymerization starting from aspartic acid precursors such as maleic acid ammonium salt (EP 0 256 366), maleic amide (EP 0604 813) and maleic anhydride, and ammonia-releasing compounds.